Growth of Listeria monocytogenes at 10°C in Milk Preincubated with Selected Pseudomonads

Abstract

Preliminary studies involving co-inoculation of Listeria monocytogenes with Pseudomonas fragi into whole or skim milk demonstrated that neither inhibition nor stimulation of growth occurred for either organism. Additional investigations involved preincubation of whole milk, skim milk, and 10% reconstituted nonfat dry milk (NDM) for 3 d at 10°C with P. fragi, Pseudomonas fluorescens P26, P. fluorescens T25, or P. fluorescens B52, followed by inoculation with L. monocytogenes and further incubation at 10°C. Growth curves of L. monocytogenes were constructed for each treatment combination and generation times were statistically compared for differences. Results indicated that L. monocytogenes did not affect growth or survival of the preincubated Pseudomonas spp. However, growth rates of L. monocytogenes were significantly (P<0.05) enhanced in milks preincubated with pseudomonads. Doubling times of L. monocytogenes were reduced by up to 3 h when grown in milk preincubated with Pseudomonas spp. Three strains o...